Magnetic nitride film

ABSTRACT

The disclosed magnetic nitride T-M-N film (T is at least one metal selected from the group consisting of Fe, Co, Ni and Mn; M is at least one metal selected from the group consisting of Nb, Zr, Ti, Ta, Hf, Cr, W and Mo; N is nitrogen (N)) has excellent wear resistance and high electric resistivity, and the compositionally modulated nitride film shows a soft magnetic property, as well as thermal stability of the properties.

This is a continuation of application Ser. No. 07/279,715, filed12/5/88, which was abandoned upon the filing hereof; which is Cont. ofSer. No. 07/024,141, filed Mar. 10, 1987, now U.S. Pat. No. 4,836,865.

FIELD OF THE INVENTION AND RELATED ART STATEMENT

1. FIELD OF THE INVENTION

The present invention relates generally to a soft magnetic nitride film,and more particularly, to a soft magnetic nitride film suitable for useas a magnetic head or the like.

2. DESCRIPTION OF THE RELATED ART

Heretofore, there have been attempts to produce magnetic alloy filmscontaining nitrogen (N) by N₂ reactive sputtering or by sputtering usinga nitride target. For example, a nitride alloy film made of Fe, Co, Niand glass-forming elements such as B, Si, Al, P, and C (shown inJapanese published unexamined patent application Nos. Sho 54-94428 and60-15261) and an iron nitride film (shown in the Journal of AppliedPhysics (J. Appl. Phys.) 53(11), 8332(1982)) are well known. In the caseof the former, for example, in a nitride Fe-B-N film made by nitrifyingFe-B alloy, the perpendicular magnetic anisotropy increases, andaccordingly, the soft magnetic property of the Fe-B alloy deteriorates.At the same time, the saturation magnetization (hereinafter referred toa the value of 4πMs) decreases by the nitriding thereof. On the otherhand, in the case of the Fe-N film of the latter, when the N content inthe Fe-N film is small, the value of 4πMs increases, but the coerciveforce, Hc, is large, and accordingly, the Fe-N film does not exhibit asoft magnetic property. Accordingly, at the present time, the hardmagnetism of the Fe-N film draws more attention than the soft magnetismthereof, and research for applying it to a recording media hasproceeded.

OBJECT AND SUMMARY OF THE INVENTION

The present invention is intended to solve the above-mentioned problems,and to provide a magnetic nitride film which has a small coercive force,Hc, soft magnetism, thermal stability of the characteristic, high wearresistance and the very high electric resistivity which is proper to anitride.

The magnetic nitride film of the present invention is represented by theformula:

    T.sub.X M.sub.Y N.sub.Z . . .                              (1)

wherein,

T is at least one metal selected from the group consisting of Fe, Co, Niand Mn; M is at least one metal selected from the group consisting ofNb, Zr, Ti, Ta, Hf, Cr, W and Mo; N is elemental nigrogen, and

X, Y and Z show the atomic percent of T, M and N, respectively, and thevalues of X, Y and Z are defined by the following expressions: ##EQU1##

Although a film having the composition indicated by the above-mentionedformula (1) is a nitride, when the value of Z is defined by expression(3),

    Z≦20 . . .                                          (3)

deterioration of the value of 4πMs is negligibly small in comparisonwith a non-nitride alloy film (i.e., Z=0), and furthermore, when thenitrogen content of the film is in this range, as the nitrogen contentincreases, the value of 4πMs, increases. Moreover, even with nitriding,when the elemental nitrogen (N) content is in the range given byexpression (3), deterioration of the soft magnetic property of thenitride film is smaller than in conventional nitride film. In order toimprove wear resistance by nitriding, a composition defined byexpression (4) is required:

    0.1≦Z . . .                                         (4).

In order to attain an excellent soft magnetic property, a requirementdefined by expression (5) must be satisfied:

    6≦Y (i.e., X<94) . . . (5).

When it is intended to apply the magnetic nitride film to a magnetichead, in order to realize 4πMs≧5000 Gauss, a condition defined byexpression (6) is required:

    75≦X (i.e., Y<25) . . . (6).

Moreover, a multilayered film is obtained by alternately laminating themagnetic nitride film and the non-nitride alloy film shown by expression(7):

    T.sub.X' M.sub.Y'  (X'+Y'=100, 75≦X'<94, 6<Y'<25) . . . (7).

This multilayered film shows excellent wear resistance and asatisfactory soft magnetic property. When the condition that t≦1000 Å issatisfied (t is the thickness of one layer), the magnetic layered filmshows remarkable effects based on the multilayer configuration, suchthat partial wear between T_(X) M_(Y) N_(Z) film and T_(Y) M_(Y) film ishardly observed, and an excellent soft magnetic property is obtained.

That is, the soft magnetic property, which is liable to be damaged bynitrifying, is retained by the alternate lamination of the magneticnitride film and the amorphous alloy film (e.g., U.S. Pat. No.4,437,912) which is designated by expression (7) and which has anexcellent soft magnetic property.

The multilayered film obtained in this way shows an excellent softmagnetic property in its prepared state. However, when it is annealed atabout 300° C., the excellent soft magnetism deteriorates due to theinterdiffusion of elemental nitrogen (N) between the layers.

Such thermal instability can be improved when the multilayered film isformed into a compositionally modulated film shown by expression (8)below by high temperature annealing. When it is used at a temperaturelower than the annealing temperature, the soft magnetic property isstable.

The compositionally modulated film, which is obtained by annealing amultilayered film composed of a nitride film and a non-nitride alloyfilm, has a composition defined by expression (8):

    T.sub.X M.sub.Y N.sub..sub.Z . . . (8)

wherein X Y Z and X+Y+Z are defined by expression (9):

    65≦X≦94

    5≦Y≦25

    0.1≦Z≦20

    X+Y+Z=100                                                  (9)

This compositionally modulated nitride film has a structure wherein thevalues of X, Y and Z are not constant throughout the direction of thefilm thickness, but are modulated periodically. The average compositionsof X, Z and Z shown by expression (8) agree with the values of X, Y andZ given by expression (2) throughout the multilayered film.

As mentioned above, since the compositionally modulated film has astable structure, interdiffusion hardly causes a change incharacteristic. The compositionally modulated film has thermalstability, and furthermore, has a small coercive force, Hc. Moreover, bycontaining the elemental nitrogen (N) throughout the film, excellentwear resistance and comparatively high electric resistivity can beobtained.

A feature of the composite film of the present invention is that it isneither a single layered nitride alloy film nor a multilayered alloyfilm, but is a compositionally modulated magnetic nitride film, whereinthe soft magnetism is thermally stable, and interdiffusion is hardlycaused. The excellent soft magnetic property which has never beenobtained by a single layered nitride film can thus be obtained by thecompositionally modulated structure.

Hereinafter, in showing the composition of the compositionally modulatednitride film, an average composition is given, and therein the values ofX, Y and Z are periodically modulated in the direction of the filmthickness. When a modulation wave length, λ, is defined by themodulation periodicity of the contents of the film, as λ decreases, thecoercive force, Hc, of the compositionally modulated film decreases.Particularly, when the wave length, λ, is<1000 Å, the above-mentionedeffect is remarkable.

The present invention is made, based on the fact that in expression (8),the elements represented by M (Nb, Zr, Ti, Ta, Hf, Cr, W and Mo) formmore a nitride more easily than do the elements represented by T (Fe,Co, Ni and Mn). The soft magnetic nitride compositionally modulated filmhaving a small coercive force, Hc, and thermal stability is obtained byannealing a multilayered film using this tendency, wherein elementalnitrogen (N) is mainly compositionally modulated. Hereupon, thethermally stable film is a film which has a compositionally modulateddepth profile wherein the contents of the M and N elements vary amost inphase, and the contents of the T element vary in an opposite phasebecause of the difference in the affinity between T-N and M-N. Thosesoft magnetic nitride films are thermally stable, and have acompositionally modulated depth profile. In those films, changes of theproperties due to interdiffusion hardly occur. Thus, the soft magneticnitride film having a small coercive force, Hc, which was not obtainedin a single layered nitride film, is obtainable.

Moreover, in the compositionally modulated nitride film of the presentinvention, the deterioration of the characteristic is small, even at ahigh temperature, in comparison with an amorphous alloy film having acomposition indicated by expression (7) which does not contain elementalnitrogen (N). The amorphous alloy not containing elemental nitrogen (N)is crystallized above the crystallization temperature, T_(X), and as aresult, the soft magnetic property thereof is lost and the coerciveforce, Hc, becomes larger than 10 Oe. The T_(X) of the conventionalamorphous alloy is 560° C-570° C. at highest, and the higher the valueof 4πMs is, the lower the T_(X) becomes. Accordingly, when themanufacturing of a magnetic head using the amorphous alloy is intended,it is difficult to set the temperature of the production process above500° C.

On the other hand, in the compositionally modulated nitride film of thepresent invention, after annealing at 600° C., the coercive force, Hc,is smaller than 5 Oe, and the thermal stability of the characteristic isexcellent. The single layered nitride film (a non-compositionallymodulated film) is also thermally stable, but the coercive force, Hc, iscomparatively large, both before and after annealing. Therefore, thecompositionally modulated nitride film of the present invention has abetter magnetic property than the simple non-compositionally modulatednitride film. Moreover, since the magnetic nitride films of the presentinvention have the excellent wear resistance proper to a nitride, ahigher electrical resistivity than that of conventional alloys, and athermally stable soft magnetic characteristic, they are suitable for useas the core of a high frequency magnetic head or the like.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing the relationship between saturationmagnetization and the amount of N₂ in the sputtering gas and therelationship between the coercive force, Hc, and the amount of N₂ in thesputtering gas.

FIG. 2 is a diagram showing the relationship between the amount of N₂ inthe sputtering gas and the atomic percent of elemental nitrogen (N) in anitride film made using the sputtering method.

FIG. 3 is a diagram showing the relationship between the amount ofpartial wear, (Δ1), of (Co-Nb-Zr/Co-Nb-Zr-N)^(n) multilayered film andthe layer thickness, and the relationship between the coercive force,Hc, and the layer thickness.

FIG. 4(a) and FIG. 4(b) are diagrams showing depth profiles of thecompositionally modulated nitride film of the present invention.

FIG. 5(a) and FIG. 5(b) are diagrams showing depth profiles measured byAuger electron spectroscopy.

FIG. 6(a), FIG. 6(b) and FIG. 6(c) are diagrams showing the B-H loops ofan amorphous alloy film, a compositionally modulated nitride film and anitride alloy film measured before and after annealing at 620° C.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Example 1

Nitride films, which were 1 μm thick, were made using the N₂ reactivesputtering method, wherein a target with a composition of Co₈₅ Nb₁₀ Zr₅and a mixed gas of Ar and 0.1-50% N₂ were used. For comparison,comparative nitride films were made using the same sputtering methodwith two kinds of targets, Fe and Fe₈₀ B₂₀. The characteristics of thenitride films of the present invention and the comparative nitride filmsare shown in FIG. 1. As clearly shown in FIG. 1, in the magnetic nitrideCo-Nb-Zr-N film of the present invention, deterioration of the softmagnetism was comparatively small, even after nitriding thereof; andfurther, the value of 4πMs did not decrease by nitriding, but showed amaximum at X=10%, and an increase in the value of 4πMs was observedaround X=10%.

From FIG. 1 and FIG. 2 showing the results of the analysis, it wasproved that in a nitride film containing elemental nitrogen (N) in anamount less than about 20%, the coercive force, Hc, was comparativelysmall and the value of 4πMs did not decrease. Therefore, the nitridefilm of the present invention is a suitable soft magnetic material whichmay be used as a magnetic head.

On the other hand, in a metal-metalloid system, as shown in FIG. 1, thevalue of 4πMs of Fe-B-N decreased comparatively quickly with nitriding,and furthermore, the coercive force, Hc, largely increased withnitriding, in comparison with the nitride Co-Nb-Zr-N film of the presentinvention. Moreover, in an iron nitride (Fe-N) film, the value of 4πMsslightly increased for a certain range of elemental nitrogen (N) contentin comparison with a non-nitride iron film, but the coercive force, Hc,was extremely large, and therefore, it was not a suitable soft magneticmaterial which could be used as a magnetic head.

Example 2

Multilayered films composed of Co-Nb-Zr film and Co-Nb-Zr-N film weremade by using the same target as in Example 1. The films were preparedby sputtering, while introducing 10% N₂ gas into Ar gas periodically. Bychanging the sputtering period wherein N₂ gas was mixed in sputteringgas, the thickness, t, of the Co-Nb-Zr-N layer was varied. Furthermore,by setting the period of sputtering in the sputtering gas not containingN₂ gas to be equal to the period of sputtering in the sputtering gascontaining N₂ gas, the thickness, t', of the non-nitride Co-Nb-Z layerwas adjusted to be almost equal to the thickness, t, of the nitridelayer (Co-Nb-Zn-N). (Strictly speaking, t', was slightly thicker thant.) Resultant multilayered films had a total thickness of about 12 μm.The thickness of the layer and the number of layers in the samples wereas follows.

    ______________________________________                                        Sample  t (Å)  t' (Å)                                                                              number of layers (n)                             ______________________________________                                        1       ab. 9500    ab. 10500                                                                              n = 12                                           2       ab. 2800   ab. 3200  n = 40                                           3       ab. 1000   ab. 1000  n = 120                                          4       ab. 300    ab. 300   n = 400                                          5       ab. 100    ab. 100    n = 1200                                        ______________________________________                                    

These multilayered films were sandwiched and bonded between substrates.They were mounted on a VTR deck so that the side face thereof contactedwith tape. The amount of partial wear on the contact face was observedafter the tape had run for a hundred hours on the surface of thesandwiched film. Since the nitride layer had higher wear resistance thanthat of the non-nitrified alloy layer, partial wear, Δ1, was observed asshown in FIG. 3. The partial wear, Δ1, shown in FIG. 3 is a function ofthe layer thickness, t. Moreover, the coercive force, Hc, of themultilayered film is also shown as a function of the layer thickness, t.From FIG. 3, it is proved that Δ1 and Hc decreased with a decrease ofthe layer thickness, t, and the degree of decrease thereof is remarkablewhen the thickness is ≦1000Å.

Example 3

Various magnetic nitride films were made by sputtering, wherein variousalloy targets and various mixed gases (Ar+N₂) were used, and variouscharacteristics thereof were compared. The magnetic nitride films wereformed on a water-cooled glass substrate having a thermal expansioncoefficient of about 120×10⁻⁷ /°C. with an input power of 350 W and agas pressure of 1×10⁻² Torr, by using a radio frequency diode sputteringapparatus. The characteristics of those film are shown in Table 1.

As shown in Table 1, the hardness of the nitride films increased as theN₂ partial pressure rose, and furthermore, even when the N₂ partialpressure was 0.1%, the hardness thereof was improved.

    ______________________________________                                                  N.sub.2 Par-            Hard- Resis-                                Composition of                                                                          tial Pres-                                                                             4πMs  Hc    ness  tance                                 Target    sure (%) (Gauss)  (Oe)  (Hv)  (μΩ cm)                      ______________________________________                                        Co.sub.82 Fe.sub.2 Nb.sub.16                                                            0        10000    0.1   800   130                                             0.1      10000    0.5   850   130                                             2        10800    2     900   200                                             10       11200    4     920   600                                   Co.sub.80 Ti.sub.20                                                                     0        7000     0.1   750   120                                             2        8000     2     850   180                                             10       8600     4     880   500                                   Co.sub.85 Ta.sub.15                                                                     0        8000     0.5   780   130                                             2        8800     3     880   200                                             10       9200     6     900   600                                   Co.sub.82 Nb.sub.12 Zr.sub.6                                                            0        8000     0.05  850   130                                             0.1      8000     0.2   900   130                                             2        9100     1     950   300                                             10       9600     3     980   900                                   Co.sub.80 Mn.sub.3 Nb.sub.17                                                            0        9500     0.1   800   130                                             2        10200    2     900   200                                             10       10500    4     920   600                                   Co.sub.80 W.sub.10 Zr.sub.10                                                            0        6800     0.05  850   140                                             2        7200     1     940   250                                             10       7400     3     980   800                                   Fe.sub.88 Si.sub.12                                                                     0                                                                   8000      4        --        70                                                         0.1      17000    20    --    100                                             5        9000     100   --    200                                   Fe.sub.78 Si.sub.10 B.sub.12                                                            0        14000    1     910   140                                             2        10000    5     1000  200                                             10       5000     20    1000  900                                   Co.sub.75 Si.sub.15 B.sub.10                                                            0        7800     0.05  910   140                                             2        7500     3     1050  200                                             10       6000     8     1050  800                                   Fe        0        22000    10    --     10                                             2        24000    700   --    100                                             10       7000     600   --    800                                   ______________________________________                                    

Example 4

Multilayered nitride films having four hundred layers and a totalthickness of 12 μm, were prepared by alternately sputtering at regularintervals two kinds of sputtering gases, i.e., 10% N₂ mixed with Ar gasand pure Ar gas, thereby forming alternately laminated nitride film andnon-nitride film, each having a thickness of about 300 Å. Four hundred(400) layers in total were thus laminated (200 layers of nitride filmand 200 layers of non-nitride film). The same test described in Example2 was then performed on the multilayered film. And the results thereofare shown in Table 2.

                                      TABLE 2                                     __________________________________________________________________________           Hc (Oe)         Wear Amount, l (μm)                                                                     Partial                                                     Multi-                                                                             Single Layered                                                                        Multi-                                                                             Wear                                             Single Layered Film                                                                      Layered                                                                            Film    Layered                                                                            Amount, Δl                          Target N.sub.2 = 0                                                                        N.sub.2 = 10%                                                                       Film N.sub.2 = 0                                                                           Film (Å)                                   __________________________________________________________________________    Co.sub.82 Fe.sub.2 Nb.sub.16                                                         0.1  4     1    10      ab. 3                                                                              ab. 80                                    Co.sub.82 Nb.sub.12 Zr.sub.6                                                         0.05 3     1    6       ab. 2                                                                              ab. 50                                    Co.sub.80 W.sub.10 Zr.sub.10                                                         0.05 3     1    8       ab. 2                                                                              ab. 50                                    __________________________________________________________________________

In Table 2, the single layered film represents a film made using only asingle sputtering gas of 10% N₂ mixed with Ar gas, or pure Ar gas. Thesingle layered film has a thickness of 12 μm. The wear amount representsthe total amount of wear observed after 100 hours of running the tape.The partial wear amount represents the wear produced between a nitridefilm layer and a non-nitride film layer. As shown in Table 2, thecoercive force, Hc, of the m#, it is proved that the characteristics ofthe magnetic nitride film were improved by forming the multilayeredstructure.

Example 5

A multilayered film, in which nitride film layers and non-nitride filmlayers were periodically laminated, was formed on a ferrite substrate byusing a target having a composition of Co₈₃ Nb₁₇ (atomic %), andsputtering using N₂ mixed with Ar. The N₂ gas content in the Ar gas wasvaried according t the following predetermined partial pressures: 0.2%,5%, 10%, 20% and 40%. The nitride film layers and the non-nitride filmlayers were either 1000 Å, 250 Å and 125 Å thick, and the thickness ofthe nitride and the non-nitride film layers were almost the same. As atypical example, a depth profile (measured by AES) of the multilayeredfilm composed of nitride layers formed under a partial pressure of 5% N₂gas and non-nitride layers with a layer thickness of about 250 Å isshown in FIG. 5(a).

FIG. 5 clearly shows that the multilayered structure was formed by thenitride layers and the non-nitride layers in the above-mentionedexample. Then, multilayered nitride films obtained in this way wereannealed in a vacuum at 480° C., thereby obtaining the compositionallymodulated nitride film of the present invention. As a typical example,the depth profile (measured by AES) of the compositionally modulatedfilm obtained by annealing the multilayered film of FIG. 5(a) is shownin FIG. 4(a). From FIG. 4(a) and FIG. 5(a), it is clear that, althoughbefore the annealing, the multilayered film showed a compositionalprofile wherein the Nb content was small and the Co content wascomparatively large in the nitride layer, and on the other hand, in thenon-nitride layer, the Nb content was comparatively large and the Cocontent was small; after annealing, the multilayered film showed acompositionally modulated depth profile wherein the clear distinctionbetween the nitride layer and the non-nitride layer was eliminated bythe interdiffusion of elemental nitrogen (N), and the elemental nitrogen(N) and Nb contents varied almost in phase and the Co content varied inan opposite phase. That is, the compositionally modulated depth profileshows different inclinations before and after annealing. The reason forthe above-mentioned phenomenon is as follows: the Nb content was apt todecrease with sputtering which used a mixed gas of N₂ and Ar as thesputtering gas, as compared with sputtering which used only Ar gas, butNb was more liable to form a nitride compared with Co; therefore,compositional modulation formed due to annealing at the propertemperature. For comparison, simple nitride films (noncompositionallymodulated films) were also made by sputtering with N₂ mixed gas underthe condition that the partial pressure of N₂ was 5%, 10% and 20%. Themultilayered film, the compositionally modulated nitride film and thesimple nitride films (single-layer film and multilayered film) whichwere obtained according to the above description were annealed at atemperature of 340° C. in a rotation magnetic field.

The changes in the properties of these films before and after annealingare shown in Table 3.

                  TABLE 3                                                         ______________________________________                                                               Hc (Oe)                                                                N.sub.2  Compositional   After                                                Partial  Modulation                                                                              As    An-                                  Sam- Sample     Pressure Wave Length                                                                             Pre-  nealing                              ple  Profile    (%)      (Å)   pared 340° C.                       ______________________________________                                        a    Multilayered                                                                                0.2   2000        0.5 1                                         film                                                                     b    Multilayered                                                                             "        500         0.2   0.5                                     film                                                                     c    Multilayered                                                                              5       2000      3     12                                        film                                                                     d    Multilayered                                                                             "        500       2     8                                         film                                                                     e    Multilayered                                                                             "        250         0.5 6                                         film                                                                     f    Multilayered                                                                             10       2000      3     12                                        film                                                                     g    Multilayered                                                                             "        500       1     8                                         film                                                                     h    Multilayered                                                                             "        250       1     10                                        film                                                                     i    Multilayered                                                                             20       2000      4     14                                        film                                                                     j    Multilayered                                                                             "        500       2     12                                        film                                                                     k    Multilayered                                                                             40       2000      5     15                                        film                                                                     l    Multilayered                                                                             "        500       3     13                                        film                                                                      a'  Composi-      0.2   2000        0.5   0.5                                     tionally                                                                      modulated                                                                     film                                                                      b'  Composi-   "        500         0.2   0.4                                     tionally                                                                      modulated                                                                     film                                                                      c'  Composi-    5       2000      3     3                                         tionally                                                                      modulated                                                                     film                                                                      d'  Composi-   "        500       2     2                                         tionally                                                                      modulated                                                                     film                                                                      e'  Composi-   "        250       1     1                                         tionally                                                                      modulated                                                                     film                                                                      f'  Composi-   10       2000      4     4                                         tionally                                                                      modulated                                                                     film                                                                      g'  Composi-   "        500       2     2                                         tionally                                                                      modulated                                                                     film                                                                      h'  Composi-   "        250       2     2                                         tionally                                                                      modulated                                                                     film                                                                      i'  Composi-   20       2000      5     5                                         tionally                                                                      modulated                                                                     film                                                                      j'  Composi-   "        500       3     3                                         tionally                                                                      modulated                                                                     film                                                                      k'  Composi-   40       2000      6     6                                         tionally                                                                      modulated                                                                     film                                                                      l'  Composi-   "        500       4     4                                         tionally                                                                      modulated                                                                     film                                                                     l    Single      5       --        8     10                                        Layered                                                                       nitride                                                                       film                                                                     m    Single     10       --        10    12                                        Layered                                                                       nitride                                                                       film                                                                     o    Single     20       --        13    15                                        Layered                                                                       nitride                                                                       film                                                                     ______________________________________                                    

As shown in Table 3, the magnetic characteristic of the compositionallymodulated nitride film is stable even after annealing at 340° C., incomparison with the non-compositionally modulated multilayered film.This is because the depth profile of the compositionally modulatednitride does not change due to annealing at 340° C., while that of themultilayered film does change. For reference, the depth profiles of bothfilms after annealing at 340° C. are shown in FIG. 4(b) and FIG. 5(b).Although the characteristic of the simple nitride film is thermallystable, it does not show a soft magnetic property.

Although the N₂ partial pressure and the content of elemental nitrogen(N) in the nitride film were not necessarily in a proportional relation,according to AES analysis, when the N₂ partial pressure was 20%, thecontent of elemental nitrogen (N) in the nitride film was about 20%. Thecompositionally modulated nitride shown in Table 3 was obtained byhigh-temperature-annealing of a multilayered film, wherein the ratio ofthe thickness of the nitride film layer and the non-nitride film layerwas 1:1. The average content of elemental nitrogen (N) of samples k' and1' were about 20%. When the content of elemental nitrogen (N) was morethan 20%, the nitride film easily exfoliated from the substrate, and thevalue of 4λMs decreased, and therefore, this film was of no practicaluse. Moreover, as shown in Table 3, the shorter the compositionalmodulation wave length, λ, became, the smaller the coercive force, Hc,became. Therefore, it is preferable that the λ is less than 1000 Å.

Example 6

A conventional Co-Nb amorphous alloy film was prepared by sputtering inpure Ar, using the same target as that of Example 5. The hardness andelectric resistivity of this amorphous alloy film were measured, and theresults are shown in Table 4, together with those of the compositionallymodulated nitride film prepared in the Example 5.

                  TABLE 4                                                         ______________________________________                                                         N.sub.2 Partial                                                                         Conduc-                                                                              Hard- Ratio of                              Sam-             Pressure  tivity ness  Amount                                ple  Sample Profile                                                                            (%)       (μΩ/cm)                                                                     (Hv)  of Wear                               ______________________________________                                        p    Non-        0         110    700   1                                          compositionally                                                               modulated                                                                     amorphous                                                                     alloy film                                                               b'   Compositionally                                                                             0.2     120    750   0.8                                        modulated                                                                     nitride film                                                             d'   Compositionally                                                                           5         140    750   0.5                                        modulated                                                                     nitride film                                                             g'   Compositionally                                                                           10        170    800   0.4                                        modulated                                                                     nitride film                                                             j'   Compositionally                                                                           20        200    800   0.3                                        modulated                                                                     nitride film                                                             l'   Compositionally                                                                           40        280    850   0.3                                        modulated                                                                     nitride film                                                             ______________________________________                                    

The nitride film was prepared on the top surface of a head chip-shapedsubstrate, and then mounted on a commercial VTR deck. A tape was run onthe nitride film for five hundred hours, and thereafter, the amount ofwear was observed. Table 4 shows the ratio of the amount of wear of thecompositionally modulated nitride film to that of a simple amorphousfilm.

As shown in Table 4, the compositionally modulated nitride films of thepresent invention were harder, and had greater electric resistivity andwear resistance than the conventional non-nitride amorphous film.Although the multilayered film composed of a nitride film and anon-nitride film had better wear resistance than the conventionalnon-nitride amorphous film, there was a problem in the generation ofpartial wear, since there was a difference between the wear resistancesof the nitride layer and the non-nitride layer. On the other hand, inthe compositionally modulated nitride film, partial wear hardlyoccurred.

Example 7

Using various kinds of targets, various compositionally modulatednitride films were prepared in the same way as in Example 5. Thecharacteristics of the compositionally modulated nitride films are shownin Table 5.

                                      TABLE 5                                     __________________________________________________________________________                     Compositional Hc (Oe)                                                         Modulation Wave                                                                        4πMs                                                                            Before                                                                              After Annealing                          Sample No.                                                                          Average Composition                                                                      Length (Å)                                                                         (Gauss)                                                                            Annealing                                                                           at 340° C.                        __________________________________________________________________________    1     Co.sub.94 Zr.sub.5 N.sub.1                                                               500      15500                                                                              2.5   2.5                                      2     Co.sub.90 Nb.sub.5 Hf.sub.3 N.sub.2                                                      500      14000                                                                              1.0   1.0                                      3     Co.sub.88 Ta.sub.6 Zr.sub.3 N.sub.3                                                      500      13000                                                                              1.5   1.5                                      4     Co.sub.85 Nb.sub.8 Zr.sub.4 N.sub.3                                                      500      12000                                                                              0.6   0.6                                      5     Co.sub.80 Nb.sub.8 Ti.sub.8 N.sub.4                                                      250      11000                                                                              0.4   0.4                                      6     Co.sub.76 W.sub.8 Zr.sub.8 N.sub.8                                                       500      10000                                                                              1.5   1.5                                      7     Co.sub.76 Mo.sub.4 Cr.sub.4 Zr.sub.8 N.sub.8                                             500      10000                                                                              3.5   4.0                                      8     Co.sub.70 Fe.sub.2 Nb.sub.20 N.sub.8                                                     250       8000                                                                              1.5   1.5                                      9     Co.sub.70 Mn.sub.3 Nb.sub.19 N.sub.8                                                     250       8500                                                                              1.5   1.5                                      10    Co.sub.68 Ta.sub.12 Hf.sub.8 N.sub.12                                                    250       7500                                                                              2.0   2.0                                      11    Co.sub.64 Ni.sub.10 Zr.sub.10 N.sub.16                                                   500       7500                                                                              3.0   3.0                                      12    Co.sub.65 Ta.sub. 10 Zr.sub.5 N.sub.20                                                   250       7000                                                                              4.0   4.0                                      __________________________________________________________________________

As shown in Table 5, in the compositionally modulated nitride film, thevalue of 4πMs was large and the soft magnetic characteristic wasthermally stable.

Example 8

Using Co₈₂ Nb₁₂ Ta₂ Zr₄ alloy as the target, a compositionally modulatednitride film, wherein the average content of elemental nitrogen (N) was5% and the compositional modulation wave length, λ, was 500 Å, wasmanufactured in the same manner as in Example 5. For reference, usingthe same target, an amorphous alloy film was manufactured by sputteringwith pure Ar gas, and a nitride film was manufactured by sputtering withAr gas containing 5% N₂. Those samples were annealed in a vacuum at 620°C. for thirty minutes, following which the stability of the respectivemagnetic characteristics was examined. B-H loops in 60 Hz measuredbefore and after annealing are shown in FIG. 6. In FIG. 6, (a), (b) and(c) show the B-H loops of the non-nitride amorphous film, thecompositionally modulated nitride film and the single layered nitridefilm, respectively. As shown in FIG. 6(a), the non-nitride amorphousfilm lost the soft magnetic property with annealing, since thenon-nitride amorphous film was completely crystallized by annealing. Forthe single layered nitride film (c) in FIG. 6, deterioration of thecharacteristic due to annealing was small, but there was the problem ofthe large coercive force, Hc. On the other hand, as shown in FIG. 6(b),in the case of the compositionally modulated nitride film, the softmagnetism was maintained after the annealing, and it was found that theproperty was thermally stable.

As mentioned above, though the magnetic nitride film of the presentinvention is of a nitride composition, the deterioration of saturationmagnetization is small, and furthermore, there are some cases where thesaturation magnetization increases. Moreover, the magnetic nitride filmof the present invention is superior in the thermal stability of thecharacteristic over the conventional amorphous alloy, and has both ahigh wear resistance and the high electric resistivity proper to thenitride. Particularly, the compositionally modulated nitride film showsthe soft magnetic property and high thermal stability. Therefore, themagnetic nitride films of the present invention are suitable for use asa core material of magnetic head or the like.

We claim:
 1. A soft magnetic nitride film, on a substrate, consisting ofa composition having formula:

    T.sub.X M.sub.Y N.sub.Z

wherein T is at least one metal selected from the group consisting ofFe, Co, Ni and Mn; M is at least one metal selected from the groupconsisting of Nb, Zr, Ti, Ta, Hf, W and Mo; N is nitrogen (N), and X, Yand Z show atomic percent of said T, M and N, and values of X, Y and Zare defined by the following expressions

    7≦ X<94,

    6≦Y<25,

    0.1≦Z<20 and

    X+Y+Z=100.